In general, a medium-sized battery pack including a plurality of battery cells is primarily used as a power source of an electric bicycle or an electric motorcycle. The battery pack includes a plurality of rechargeable battery cells, a housing for accommodating the plurality of rechargeable battery cells, and a battery monitoring system (BMS) board for monitoring the plurality of rechargeable battery cells.
The battery cells are typically lithium ion batteries, lithium polymer batteries, or lithium ion polymer batteries, and the housing may be made of a plastic-injected material. In addition, the BMS board is electrically connected to the battery cells to control charge and discharge of the battery cells and to calculate the capacities of the battery cells. Further, the BMS board includes a connector to be electrically connected to an external device (e.g., a charger or a load).